The research deals with platelet adhesion in arteries, focusing on an adhesion receptor, platelet glycoprotein (GP) lb. The long-term objective is to characterize genes, genetic defects, transcripts and polypeptides that relate to GP lb. Circulating platelets function as monitors of the endothelial lining of blood vessels, sticking to areas with exposed subendothelium. At sites of vascular injury, platelet adhesion or "sticking" initiates normal platelet plug formation that stops blood loss. At sites of vascular disease, however, platelet adhesion sets off abnormal thrombosis that leads to heart attacks and strokes. In the arterial circulation, platelet surface glycoprotein lb serves as the contact point for adhesion by binding von Willebrand factor and using it as a link to the vascular surface. Two other surface glycoproteins, GP V and GP IX, are related to GP lb through common structural elements (leucine-rich glycoprotein sequences) and a common congenital deficiency state (Bernard-Soulier syndrome). GP lb and GP IX associate directly in the GP lb-IX complex. Stemming from four genes (lb alpha/lb beta/V/IX) dispersed on separate chromosomes, the three proteins, GP lb/V/IX appear to work in concert to produce a functional surface GP lb receptor. This proposal asks, "What relationships coordinate the lb/V/IX system?" "Do the genes share common structures, particularly promoters?" "Does a common mechanism regulate gene expression?" "Can one gene defect cause a congenital deficiency of the three surface GP's?" "Can transfected cDNAs produce a mature surface GP lb receptor?" Specific Aims and Experimental Approach 1. Clone and characterize the cDNA encoding human platelet glycoprotein V. 2. Clone and characterize genomic DNA encoding glycoproteins Ibbeta, V, and IX. 3. Characterize the genetic defect in two cases of Bernard Soulier syndrome. 4. Characterize the transcriptional response of the lbalpha, lbbeta, V, IX genes. 5. Assess the structure and function of lbalpha using transfected cDNAs.